In masonry construction, consecutive horizontal rows of building stones are laid on top of one another. After a row is completed in this process, a layer of binding cement, such as mortar or adhesive, is spread over its top side. A reinforcement strip is then laid on top of this layer, and then a layer of binding cement is again spread over the top side of this reinforcement strip such that the two layers then flow into one another through the mesh of the grid, which results in the creation of one single layer of binding cement with the reinforcement strip imbedded in it. The following row of building stones is then laid on top of this, such that a horizontal joint is created between the previous and the subsequent row of building stones. This joint is thus reinforced against the development of vertical cracks which would tend to run through this joint. If the row of building stones is longer than the length of one reinforcement strip, then of course more reinforcement strips are laid end to end with a certain amount of overlapping to assure the continuity of the reinforcement. Care is then taken that the breaks in the reinforcement strips in successive joints be then situated so as to be staggered in relation to one another.
In order to be adapted for the reinforcement of such horizontal masonry joints, such strips have a breadth of approximately 0.6 to 0.9 times the thickness of the wall they are intended to reinforce, which means a breadth on the order of between 3 cm and 30 cm, and usually between 5 cm and 18 cm. A practical length for ease of handling on the work site is in the range between 2 and 7 meters. In general, they are completely flat, but this does not mean they cannot contain indentations projecting outside this flat plane, which could then fit into the cavity of the wall or into vertical openings in or between the building stones. Further, in order to be adapted for the reinforcement of horizontal masonry joints, the mesh structure of the strip needs to be open enough to permit the mortar, adhesive or other binding cement sufficiently to flow through the grid when the building stones are laid, in such a manner that, in the joint between the two adjacent rows of building stones, a single layer of binding cement can be formed, that joins the two rows of building stones with one another and in which the structure is embedded. And finally, in order to be adapted for the reinforcement of horizontal masonry joints, a number of the steel wires which are part of the mesh structure, must each run straight in the longitudinal direction from the one longitudinal end of the strip to the other, have a cross-section ranging between 6 and 20 mm.sup.2 and a steel tensile strength of more than 450 N/mm.sup.2. These are the reinforcement wires. The remaining wires of the grid then serve to join together these longitudinally running reinforcement wires into a single piece in the form of a grid-shaped strip. The whole of these remaining wires is here called the steel wire connecting structure. This connecting structure can take on a great variety of different forms, for example consisting of a number of separate cross-wires which are welded to the reinforcement wires on both sides to form a ladder structure or, by preference, consisting of one single zigzag wire, as will be given as an example below. Viewed separately, without the reinforcement wires, this connecting structure can thus in and of itself form either a number of interconnected units, or a collection of separate wires. The invention will not be limited to any specific embodiment of this connecting structure, although the embodiment as one single zigzag wire will be the preferred embodiment.
A usual embodiment for such a grid-shaped reinforcement strip is the one in which the strip contains two straight and continuous steel reinforcement wires with round cross section, running in parallel in the longitudinal direction of the strip and at a distance from each other and forming the side edges of the strip, both thus adjacent reinforcing wires being connected with one another by means of a steel wire connecting structure which is spot welded on both sides to the mutually facing sides of said adjacent reinforcement wires. This connecting structure consists preferably of one single continuous steel wire with a round cross-section, which runs from the one longitudinal end of the strip to the other in a V-shaped zigzag line running back and forth from one contact location on the inner side of one of the two adjacent reinforcement wires to a contact location on the inner side of the other adjacent reinforcement wire, in which the wire is spot welded at the successive contact locations to the respective reinforcement wires. Here, the inner side of a reinforcement wire is the side which faces the adjacent reinforcement wire. By preference, the reinforcement wires are knurled to effect good adhesion with the binding cement. In such case, the wires in this strip have a diameter in the range of from 3 to 4 mm. Since the zigzag wire, or more generally the steel wire connecting structure, is spot welded on the inner sides of the reinforcement wires and not on the upper or under sides, the thickness of the strip is equal to the diameter of the wires.
In order to make it possible to obtain masonry with thinner joints, a method is known from GB 1 403 181 where such strips, after welding the wires with round cross-section, are rolled into a flattened shape. A reinforcement strip is thus obtained in which the zigzag wire and the two reinforcement wires of the strip have been flattened in the plane of the strip to a thickness which can be less than 1.75 mm and with a thickness-breadth ratio which can be less than 0.3.
The aim of the invention is to provide a reinforcement strip, also with a flattened shape but with a structure, which offers a number of advantages and further, although not limited thereto, is suitable for being made in very thin form of execution, also of less than 1.75 mm and with a thickness-breadth ratio which can be less than 0.3. Here, the number of reinforcement wires in the strip need not necessarily be limited to two, and thus there can be more than two reinforcement wires present in the strip. Between each two wires of each distinguishable pair of adjacent reinforcement wires, then, there is a corresponding part of the steel wire connecting structure, which is not necessarily limited to a wire running in a V-shaped zigzag line.
In the reinforcement strip according to the invention the reinforcement wires have also a flattened shape in the plane of the strip, preferably with a thickness which is less than 1.75 mm and a thickness-breadth ratio which is less than 0.3, and this strip is further characterized by the fact that the spot welds have an unflattened structure and that said steel wire connecting structure comprises a number of steel wires having a thickness which is not greater than that of said reinforcement wires. By preference, this steel wire connecting structure consists of one single zigzag wire such as described above.
The above characteristics mean that this is a reinforcement strip which has not been made thin by means of rolling the entire piece flat, but rather by welding together what on the one hand are thin pre-flattened wires, e.g. pre-rolled bands, to serve as reinforcement wires, with what, on the other hand, are thin wires selected not to be thicker than the thickness of the bands and which serve as the connecting structure. This new concept offers a number of important advantages.
On the one hand, this concept avoids the necessity of having to roll the welds flat afterwards, which would result into flat-rolled welds with a flattened structure, i.e. the cold worked metallographic structure of a weld. In tensile-strength tests indeed of the known strips, it was observed that the breakage always occurred at such a weld, and at a tension of approximately 500 N/mm.sup.2. It therefore made no sense to give the reinforcement wires a greater tensile strength than that of their weakest spots. Due to the fact that such welds are no longer present, it becomes possible to increase the tensile strength of the reinforcement wires to 600 N/mm.sup.2 and more, though for manufacturing reasons not generally higher than 1000 N/mm.sup.2. Moreover, the flatter the earlier strips were rolled, in order to be suitable for correspondingly thinner joints, the more cold deformation there was of the welds and thus the weaker these weak spots became. Due to this fact, the flat-rolling of the strips to thickness-breadth ratios of the originally round wires of under 0.3 was not recommended, and flatter embodiments were not normally available on the market.
On the other hand, since the pre-flattened reinforcement wires in the invention can preferably be pre-rolled wires, the possibility is opened up of using rolled wires--in a preferred embodiment--that have been counter-rolled, in which then at least the sides to which the spot welds are to be applied display a flattened, roughly straight edge, approximately perpendicular to the plane of the band, in contrast to the rounded edge of a wire that as part of a reinforcement strip has been rolled flat between two rollers. This flattened edge turns out to be very useful in preventing difficulties in the welding of very thin bands to the equally thin--or even thinner--wires of the connecting structure, when these wires have a round cross-sectional shape, as preferred. The spot welding of the rounded edge of a very thin band (under 1.75 mm) with the thin round wire of the connecting structure (also under 1.75 mm) turns out to be difficult to accomplish with a sufficiently fast welding time and without the risk of burning through the thin wire because there is too little contact surface area. Thanks to the flattened inside edge, the use of thin bands and of wires under 1.75 mm and the manufacture of thin strips having a thickness of less than 1.75 mm has become much easier, in any case under economical manufacturing circumstances.
Compared with the earlier strips, which were rolled flat as a single piece, there is yet another advantage, which relates to the wires of the connecting structure. These were rolled flat to form broad bands such as are shown in the GB patent referred to above, and due to this fact, the size of the mesh opening is diminished by a not to be disregarded percentage, and it is this mesh opening through which the binding cement makes the attachment from the lowest row of building stones to the highest row. The size of this opening becomes especially important when stones are laid with very thin joints containing very little binding cement, particularly in the technique where adhesive is used as binding cement for the attachment of smooth building stones which have been fabricated in moulds. In the concept according to the invention, however, very thin round wires can now be selected with a final diameter that is not larger than the thickness of the reinforcement wires and these thin round wires are now no longer rolled flat, which would cause them to broaden.
Finally, there is a further advantage in terms of the simplicity of fabrication when one wants to roll the strips till they are very thin. In manufacturing strips that are rolled flat as a single piece, it is difficult to flatten the wires in an economical manner, more specifically when a thickness-breadth ratio of less than 0.3 is aimed at. For this purpose, it is necessary to start rolling in several passes with rolling equipment of relatively large dimensions and relatively large pressure values. The rolling of separate round wires however into bands of very flat shape, by means of continuous multiple-pass rolling in line, with the possibility of counter-rolling in the final pass, for example with a turks head, is a sufficiently common technique in already existing and known small ordinary rolling equipment, and it is a technique that has already attained a high level of reliable quality. This technique can also be utilized for flattening the reinforcement wires in the reinforcement strips of the invention. The same holds for the preferred round wires of the connecting structure, the manufacture of which by drawing to small final diameters under economical conditions being a matter of routine. Moreover, immediately after rolling and before welding, the flat sides of the reinforcement wires can be given a knurled surface which remains unchanged in the reinforcement strip as final product. In the technique in which the strip as a single piece is rolled flat, however, the knurled surface, which in some cases is introduced beforehand in the reinforcement wires, is then rolled away. If one nonetheless wishes to introduce the knurling afterwards on the strip itself, then it is difficult to prevent the strips from curling up during the knurling process. The straightening of such a strip afterwards into an acceptably straight piece is sufficiently complicated for giving up the idea of knurling the welded strip. When separate flat wires are knurled however, and they curl, the technique for straightening them into a straight shape by alternate bending between relatively small straightening rollers is a simple, well known technique which does not affect the knurling. This knurling is advantageous for a better adhesion of the reinforcement wires to the binding cement.
Here the invention will now be further explained in terms of an example and with reference to a number of figures. These include: